Lack of RAN-mediated toxicity in Huntington's disease knock-in mice

Identification of repeat-associated non-AUG (RAN) translation in trinucleotide (CAG) repeat diseases leads to an emerging concept that CAG repeat diseases are caused by non-polyglutamine products. Nonetheless, the exact contribution of RAN translation to the pathogenesis of CAG repeat diseases remains elusive. Via CRISPR/Cas9-mediated genome editing, we established new knock-in mouse models that harbor expanded CAG repeats in the mouse huntingtin gene, which express RAN translated products or polyglutamine products respectively. Here we report that RAN translation is not detected in the knock-in mouse models, and that only the expanded polyglutamine products can cause neuropathology and behavioral phenotypes. Therefore, polyglutamine products, rather than RAN translated products, play a major role in the pathogenesis of CAG repeat diseases. We performed RNA sequencing analysis using striatal tissues from 6-month old WT, E1 and KI-96 mice, each group includes at least four biological replicates.对三核苷酸（trinucleotide）重复疾病中重复相关非AUG（repeat-associated non-AUG, RAN）翻译的研究，催生了“CAG重复疾病由非聚谷氨酰胺（polyglutamine）产物致病”这一新兴概念。然而，RAN翻译对CAG重复疾病发病机制的确切贡献仍不明确。本研究通过CRISPR/Cas9介导的基因组编辑技术，构建了全新的敲入小鼠模型：这些模型在小鼠亨廷顿基因中携带扩增的CAG重复序列，可分别表达RAN翻译产物或聚谷氨酰胺产物。本研究发现，在上述敲入小鼠模型中未检测到RAN翻译，且仅扩增型聚谷氨酰胺产物可引发神经病理与行为表型异常。由此可见，聚谷氨酰胺产物而非RAN翻译产物，在CAG重复疾病的发病机制中发挥主要作用。本研究对6月龄野生型（wild type, WT）、E1及KI-96小鼠的纹状体组织开展了RNA测序分析，每组至少包含4个生物学重复样本。